Upper Big Branch Mine-South is an underground coal mining operation in Raleigh County, West Virginia, operated by Performance Coal and owned by Massey Energy.

On April 5, 2010, an explosion at the mine killed 29 miners, with two hospitalized.[1] Mine-safety experts said explosions are typically caused by high levels of methane produced during longwall mining, which mining companies try to dilute with ventilation systems, although Massey had been repeatedly cited for violating this requirement.[2] The Upper Big Branch mine had six violations related to ventilation since January and four since March 17, according to Mine Safety and Health Administration (MSHA) data. In 2009, the mine had 50 "unwarrantable failure citations," the most serious findings of negligence a mine inspector can issue. One citation was for not properly marking escape routes for miners in case of an accident. MSHA had proposed penalties of $900,000 in 2009 resulting from 458 total safety violations at the mine.[3] There have been three other fatalities at the Upper Big Branch mine in the last 12 years. Massey has managed to push the United Mine Workers union out of all of its operations except for a single processing plant.[2]

On May 2, 2011, it was reported that Massey Energy was seeking federal regulators’ approval for a plan to permanently seal the Upper Big Branch Mine.[4]